Salt feed device for alkali metal cells



Aprl 12, 1966 o. M. BROWN, JR., ETAL 3,245,899

SALT FEED DEVICE FOR ALKALI METAL CELLS Filed May 2, 1960 FIG. 2

FIG.

United States Parent O 3,245,899 SALT FEED DEVICE FOR ALKALI METAL CELLS Orland M. Brown, Jr., Baton Rouge, La., and Douglas R. King, Darien, Conn., assignors to Ethyi Corporation, New York, N .Y., a corporation of Virginia Filed May 2, 1960, Ser. No. 25,925 3 Claims. (Ci. 204-245) This invention relates to a fused salt electrolysis cell, particularly to an improved device for feeding salt into the interior of such cells.

Generally, cells for the production of alkali metals are basically similar in design to the Downs cell, U.S. 1,501,756. This cell is characterized by a bottom mounted carbon anode (or anodes) which extends upwardly into the cylindrical opening (or openings) of a steel cathode. The cylindrical opening of the steel cathode is of slightly larger diameter than the diameter of the anode so that an annular opening is formed between anode and cathode. Within the annular portion, which constitutes an electrolysis zone, is usually inserted a formaninous metal diaphragm. Into this cell is charged a salt, or mixture of salts, as for example the chloride sa-lt of an alkali metal and during electrolysis decomposition of the salt occurs and the chlorine is evolved from the anode and is removed from the upper portion of the cell through a gas dome situated above the anode. The alkali metal, which is separated from the salt, is displaced to the upper portion of the cell and is manifolded within an annular co-llecting chamber and removed through a vertical take ofi line or riser pipe communicating with the cell exterior.

Extremely high temperatures are required to melt alkali metal salts, especially sodium chloride, and it is therefore customary to add other salts, such as calcium chloride, to lower the melting point. At Startup a fused mixture of calcium chloride and sodium chloride is preferably employed for the manufacture of sodium. During cell operation metallic sodium and chlorine are produced, the calcium chloride remaining within the molten bath. It is thus necessary to supply only make-up quantities of ca lcium chloride, but it is absolutely essential to constantly supply fresh sodium chloride to the cell because metallic sodium and chlorine gas are being continuously removed from the cell in great quantity. Addition of sodium chloride to an Operating cell however is no simple task, particularly at the extremely high temperatures of operation. This is especially so because sodium chloride does not readily dissolve when added to the molten salt bath. The sodium chloride does not wet readily and a large proportion of the partially wetted, the partially dissolved and the undissolved salt accumulates and solidifies in the bath forming large hard deposits i upon certain portions of the cell. In a very short time these deposits make further feeding of the cell impossible. These deposits also interfere with the efficiency of the cell and it is therefore absolutely essential that these deposits be periodically removed. Thus, generally hourly, it is customary within a commercial establishment for some of the Operating personnel to make the rounds to dislodge these sodium chloride deposits. This is done by the use of crowbars or similar instruments which are used mechanical-ly to dislodge the formations. The Operating personnel doing this work must stand on top of the operating cells in performing their duties. Quite obviously, this hot and tedious task is not only unpleasant but eX- tremely -hazardous It is also apparent that this isa quite costly operation, particularly in a commercial establishment employing a large number of these cells.

Because of these 'and other disadvantages it is an object of the present invention to provide a new and improved. salt feed device capable of extended operation and which does not permit any substantial accumulation of salt deposits. It is also an object of the present invention to provide a new and improved automatic salt feed device which will greatly decrease Operating costs. A further object is to provide apparatus for a more effective feeding of salt into an Operating cell. A more specific object is to provide an automatic salt feed mechanism capable of continuously feeding salt into a cell and without the formation of salt deposits.

The details of the method and, apparatus and of the preferred embodiments of this invention will more readily be understood from the following description, particularly to the more detailed description which makes reference to the accompanying FIGURES 1 and 2.

FIGURE 1 is an elevation view illustrating a preferred salt feed device and its relation to a fused salt electrolysis cell, with which it is used in combinaton, and

FIGURE 2 is a cross section through line AA showing the portion of the sa-lt feed device wherein the salt is fed and dissolved.

The invention will be better understood from the following general description.

In accordance with the present invention there is provided an improved method for dissolving salt within a molten fused bath composition which method comprises forming a comparatively small and. localized vortex upon the surface of the molten bath, feeding salt into the vortex wherein it is substantially dissolved, and then dispersing or displacing the dissolved salt outside the vortex and into the bath proper. Thus, a key and novel feature of the invention is the formation of a small whirlpool or vortex at a location upon the surface of the molten bath. The vortex or turbulent area is localized so that there is no disturbance of the main body of molten bath. When salt is fed into this rapidly moving swirling body of liquid it is wetted, dissolved and is then displaced or dispersed into the main body of the molten electrolyte or bath. An outstanding advantage of this method is that there is no disturbance of the main body of bath such as would disrupt the normal flow pattern within the cell. Furthermore, hazardous crowbar dislodgments of hard agglomera tions, or salt encrustations, which in terfere with the efi'iciency of the cell are unnecessary since the accumulation of these deposits are substantially completely eliminated.

A preferred apparatus embodiment of this invention comprises the combination of a salt feed device and a fused salt electrolysis cell having an anode and cathode contained within a surrounding cell shell to form an anode-cathode chamber which is filled with a molten fused electrolyte. The salt feed device comprises an upwardly opening hollow or tubular member having side walls within the confines of which is fitted a stirring device. The walls of the hollow member are of a cross section less than that of the surrounding cell shell which forms the anode-cathode chamber. The lower portion of the hollow member, including the stirring device, are immersed within the molten electrolyte. Fresh salt fed into the hollow member is dissolved within the agitated molten bath contained within the hollow member, is dissolved, and is then dispersed or displaced to the main body of the molten electrolyte.

These features and advantages will be better understood from the following detailed description of the invention and its preferred embodiment.

The general disposition of the apparatus of the present invention within a sodium cell is illustrated by FIGURE 1 as above mentioned. Referring to FIGURE 1, the principal Components of a cell include a centrally bot-tom m-ounted anode 12 surrounded by a cylindrical cathode 13. The anode 12 and -cathode 13 are contained within a surrounding cell shell 11 lined with refractory material to form electrolyte retaining means. A molten electrolyte 31 is contained within the confines of the cell shell 11. The molten electrolyte submerges the electrodes to form an anode-cathode chamber, The cathode 13 is connected through the arms 14 to the bus bars 15 which provide a source of electric current. The current is fed to the anode 12 by means of the anode bus bar 16. A dome and collector assembly 18 is mounted above the anode 12 and cathode 13 to receive and to collect the products of electrolysis. Thus, the metallic sodium produced is collected and manifolded within the conduit 19 and is then discharged through the riser pipe 21, upon which are located the cooling fins 22. Gaseous chlorine rises within the dome 17 and is conveyed through line 20 for collection.

FIGURE 1 also shows the salt feed device or electrolyte makeup means mounted upon the cell. Salt is fed into the cell through the salt conduit 45. The flow of salt through this conduit 45 can be Conveniently regulated by means of the diaphragm valve 41. The pressure responsive diaphragm valve 41 opens, closes or restricts the orifice opening 44 by movement of the tapered plug 43 which is operatively connected to the diaphagram through stern 42. The diaphragm valve 41 is generally connected to a liquid level control device (not shown) which regulates the flow of salt in response to the liquid level of the molten electrolyte 31.

Salt from the conduit 45 is fed into the hopper 46 and then into the tubular member or draft tube 53 whereby the salt is introduced beneath the surface of the electrolyte. Within the confines of the tubular member 53 is contained the lifter turbine impeller or mixing means 52. The turbine stirring device is preferably of the lifting type and includes a circular disc 56 preferably of slightly smaller diameter than the diameter of the cross section of the tubular member 53 so as to partially close the lower portion of the tubular member 53 from the main body of electrolyte 31 into which it discharges via outlet port 58. Upon the upper face of the circular disc is afiixed a series of straight vanes or blades 57. The circular disc 56 is mounted upon a central spindle 51 which in turn is -operatively connected to a motor (not shown) for imparting rota-tional motion. Spindle means 51 is supported by journal means 59. To expedite the ready availability of a portion of the electrolyte 31 within the confines of the draft tube 53, serrations 54 are provided. The salt feed hopper 45 and the tubular member 53 are maintained in registered alignment upon the cell by suitable connections 47, 55, to beams 50, 48, 49 which are mounted upon the upper portion of the cell shell 11.

Referring to FIGURE 2 is shown an offset section AA through the tubular member 53 and stirring device 52. A cutter blade 61 for removing any possible salt deposits from the shaft 51 is shown mounted adjacent the shaft 51. The blade 61 is suitably mounted upon connect ions 62, 63 which are bolted together by the bolt 64 and nut 65.

A battery of twelve of the automatic salt feed devices as illustrated by reference to the foregoing figures and to the detailed description thereof was placed in operation upon an equal number of cells for a period of two months. At the end of this time absolutely no undesirable salt deposits had been formed and as a consequence the usual crowbar dislodgment Operations were eliminated entirely.

From the foregoing description it is quite apparcnt that the inventive concept and its apparatus embodiments are subject to considerable variation without departing from the spirit and scope 'of the invention, and accordingly a reasonably wide range of equivalents are possible within the metes and bounds of the described invention.

Having described the invention what is claimed is:

1. In combination with a fused salt electrolysis cell for the production of sodium having an anode and cathode contained within a surrounding cell shell to form an anode-cathode chamber, said chamber being filled with molten electrolyte, the improvement comprising a salt feed hopper in registered alignment above an upwardly opening tubular member within which is fitted a lifting turbine type stirring device, the salt feed hopper and tubular member being rigidly affixed upon the cell through suitable connections, the tubular member having serrated vertical side walls of cross-section substantially less than that of the anode-cathode chamber and being fitted within the confines of said chamber, the turbine stirring device being fitted at the lower end of the tubular member and including a circular disc of slightly smaller diameter than the diameter of the crosssection of the tubular member so as to partially close the lower portion of the tubular member, said circular disc having a series of vanes afiixed upon its upper face and being afi iXed at its center to a central spindle which is projected into the opening within the tubular member from above, the lower portion of said tubular member and turbine being mmersed within the molten electrolyte and the upper portion of said member is in open communication with the surface layer of electrolyte which is allowed to flow therein whereby salt when fed from the hopper into the vortex of the circulating molten bath within the upwardly opening tubular member is dissolved by contact with the agitated molten bath within the tubular member as induced by rotation of the turbine which discharges into the main body of the molten electrolyte.

2. In combination with a fused salt electrolysis cell having an anode and cathode contained within a surrounding cell shell to form an anode-cathode chamber, said chamber being filled with molten electrolyte, the improvement comprising an upwardly opening tubular member within whi-ch is fitted a turbine type stirring device, the tubular member being rigidly aflixed upon the cell through suitable connections, the tubular member having serrated vertical side walls of cross-section substantially less than that of the anode-cathode chamber and being fitted within the confines of said chamber, the turbine stirring device being fitted at the lower end of the tubular member and including a circular disc of slightly smaller diameter than the diameter of the crosssection of the tubular member so as to partially close the lower portion of the tubular member, said circular disc having a series of vanes afxed upon its upper face and being affixed at its center to a central spindle which is projected into the opening within the tubular member from above, the lower portion of said tubular member and turbine being mmersed within the molten electrolyte and the upper portion of said member in open communication with the surface layer of electrolyte which is allowed to flow therein, whereby salt when fed into the vortex of the circulating molten bath within the member is dssolved by contact with the agitated molten bath within the tubular member as induced by rotation of the turbine which discharges into the main body of the molten electrolyte.

3. The apparatus of claim 2 wherein said turbine type stirring device is a lifting turbine type stirring device.

References Cited by the Examiner UNITED STATES PATENTS 2,690,421 9/ 1954 Lilliendahl et al. 204-245 WINSTON A. DOUGLAS, Pr'mary Exam'ner.

JOSEPH REBOLD, Examiner. 

1. IN COMBINATION WITH A FUSED SALT ELECTROLYSIS CELL FOR THE PRODUCTION OF SODIUM HAVING AN ANODE AND CATHODE CONTAINED WITHIN A SURROUNDING CELL SHELL TO FORM AN ANODE-CATHODE CHAMBER, SAID CHAMBER BEING FILLED WITH MOLTEN ELECTROLYTE, THE IMPROVEMENT COMPRISING A SALT FEED HOPPER IN REGISTERED ALIGNMENT ABOVE AN UPWARDLY OPENING TUBULAR MEMBER WITHIN WHICH IS FITTED A LIFTING TURBINE TYPE STIRRING DEVICE, THE SALT FEED HOPPER AND TUBULAR MEMBER BEING RIGIDLY AFFIXED UPON THE CELL THROUGH SUITABLE CONNECTIONS, THE TUBULAR MEMBER HAVING SERRATED VERTICAL SIDE WALLS OF CROSS-SECTION SUBSTANTIALLY LESS THAN THAT OF THE ANODE-CATHODE CHAMBER AND BEING FITTED WITHIN THE CONFINES OF SAID CHAMBER, THE TURBINE STIRRING DEVICE BEING FITTED AT THE LOWER END OF THE TUBULAR MEMBER AND INCLUDING A CIRCULAR DISC OF SLIGHTLY SMALLER DIAMETER THAN THE DIAMETER OF THE CROSSSECTION OF THE TUBULAR MEMBER SO AS TO PARTIALLY CLOSE THE LOWER PORTION OF THE TUBULAR MEMBER, SAID CIRCULAR DISC HAVING A SERIES OF VANES AFFIXED UPON ITS UPPER FACE AND BEING AFFIXED AT ITS CENTER TO A CENTRAL SPINDLE WHICH IS PROJECTED INTO THE OPENING WITHIN THE TUBULAR MEMBER FROM ABOVE, THE LOWER PORTION OF SAID TUBULAR MEMBER AND TURBINE BEING IMMERSED WITHIN THE MOLTEN ELECTROLYTE AND THE UPPER PORTION AND SAID MEMBER IS IN OPEN COMMUNICATION WITH THE SURFACE LAYER OF ELECTROLYTE WHICH IS ALLOWED TO FLOW THEREIN WHEREBY SALT WHEN FED FROM THE HOPPER INTO THE VORTEX OF THE CIRCULATING MOLTEN BATH WITHIN THE UPWARDLY OPENING TUBULAR MEMBER IS DISSOLVED BY CONTACT WITH THE AGITATED MOLTEN BATH WITHIN THE TUBULAR MEMBER AS INDUCED BY ROTATION OF THE TURBINE WHICH DISCHARGES INTO THE MAIN BODY OF THE MOLTEN ELECTROLYTE. 